Compensated tuning fork



oct. 4, 193.2.v a E. ESENHOUR 1,880,923

COMPENSATED TUNING `FORK Filed Sept. 4. 1930 Patented Oct. 4, 1932 UNITED ASTATES PATENT OFFICE BERT E. EISENHOB, l' AURORA, ILLIQI'OIS, ABBIGNOB. OF ONE-HALF TO GEORGE FABYAN, OF GENEVA, ILLINOIS OOHPENSATED TUNING FORK appuoauoima september 4, 1930. serial No. 479,693.

The present invention relates to tuning forks, and is directed to compensatin tuning forks so that the pitch or vibration requencies thereof will remain constant irrespective` of the temperature or change of temperature of the tunin forks, or can be made any` value Within the limits of the elastic coeicients of the material used.

In a` tuning fork, the pitch or vibration 1o frequency thereof, changes with a change of length and elasticity of the material. An increase of length will cause a decrease or lowering ofthe itch or vibration frequency. A

decrease of ength will -raise or increase' the pitch or vibration frequency. A decrease of elasticity will cause a lowering or decrease in pitch or vibration frequency, and an increase of elasticity will raise or increase the pitch or vibration frequency.

Hence, when a fork is heated or rises in temperature, the fork expands and its elasticit is decreased. Both of these factors pro uce a drop in pitch. When the fork is cooled or lowered 1n temperature, the fork contracts and its elasticity increases. Both these factors raise the pitch.- These characteristics are peculiar to most materials used for making tunin forks.

Vaiious metalsnown in the trade as stoic '3 metals, such as elinvar, (invar, .and other p iron and nickel alloys) have the pro ertyof increasing and decreasing their 'e ast1c1ty a upon increase and'decrease in temperature respectively. This characteristic of stoic metals may be made to counteract the characteristics ointed out above as peculiar to the materia s usually used for making tuning forks.

An object of the present invention is to rovide a novel tuning fork composed of di erent metals havin opposite temperature coefficient values w ich will balance and main'- tain the tuning fork at a constant pitch or vibration frequency irrespective of the temperature or change of temperature of thefork. Such metals may be combined in the proportions inverselyto such values. As for example, when steel is used as one component and elin'var as the other, and if the'temp-'sra- 'ture co-ellicient values of the steel be about the particuar embodiments selected to illusten times that of the o posite temperature coeiclent .value of the ellinvar, then the result- 1ng fork may be composed in the proportions otf albout ten parts of elinvar'to one part of s ee y Other objects, advantages .capabilities and features are comprehended ythe invention as 'wlll4 later a pear and as are inherently possessed there Referring to the drawing:

Figs. 1, 2 and-3 are ers ective views of alternative forms of tuning orks constructed in accordance with the invention.

Referrinfv more in detail to the drawing,

trate the invention, are shownin the form' of laminated forks.

In Fig. 1, the fork comprises leg lamin 1, 2, 3 and 4 of which laminas 1 and 2 are connccted by the usual form of cross-head 5 carrying a stem 6.

In Fig. 2 the fork comprises leg laminas l, 2, 3, 3", 4, and 4", the cross-head also comprising cross head laminas 5, 5b and 5. The stem 6 is connected to the lamina 5.

In Fig. 3 the fork comprises le laminas. 1, 1", 2, 2", 3 and 4 cross-hea lamin 5, 5 and 5. The stem 6 is connected to the cross-head. h

In each of these, the laminas 3, 4, 3, 3", 4, 4", 3 and 4, may be of any usual material used for making tuning forks, such as steel or other similar material, while the other laminaal, 2, 1, 2, 1, 2, 1d and 2d are of material having a temperature co-eflicient value opposite to that of the steel and the like, such as invar, elinvar o1" like metals or alloys. The former laminas maybe secured to the edges of the fork (as in Fig. 1) or the sides of the fork as in Fig..2 or intermediately of the fork as in Fig. 3 in any suitable manner, as by soldering, welding, braaing, rivets, screws, and the like. f

By re nlating or adjusting the proportions and similar physical properties of the differcnt metals, 1t 1s possible to control the frequency or period of vibration of the fork when lsubjected tc changes in temperature. To secure such control, 1t is necessary that the two different metals or alloys have oppo- 100 :be lowered in a tuning fork. nee must be opposite or positive in value and F01 the pur ose of giving an example it will be assume that the laminas?) and 4 (lzig. 3", 4, and 4b (Fig. 2) and 3 and 4 3). are of steel having a temperature coe cient ofelasticity of 62.2 X 10". This is negative in value for the reason that with increase in temperature .the elasticity will de crease and hence the requenc or pitch will he other lamithe temperature coeliicient of elasticity thereof equal to that of the steel, so that an increase in temperature will effect an increase in elasticity and hence increase the frequency or pitch of the fork. With these two metals lirmly connected together, and with the different laminas tuned to. ap roximately the same frequency before assem ling, the resultvant assembly ,will have the same frequency and the systemis balanced Without stresses and strains.

If now the system be heated, the lamin having the negative value will tend to decrease the itch and the lamin having the positive va ue will tend-to increase the pitch,

vand since these opposing forces are equal,

there is no change and the entire system remains with a constant or fixed pitch or vibration frequency.

In a specific case, a tuning fork component of elinvar of given dimensions was made for a frequency of 512 D. V. and measured over a temperature range of 32 to 212 F. and the temperature coefficient of frequency found to be 5.17X10' ositive. A similar component of steel withJ a little more than one tenth the thickness of the -elinvar component was made for the same frequency and Vlikewise measured for its temperatur-e coeflicient of frequency which was found to be 62.2X10 negative. These two components were united and the resultant fork tested with the result that its temperature coelicient of frequency was 5.11X10 ne ative. This was then adjusted or regulated y removing some material from the steel coinponent to bring down the temperature coefficient of freqiency to as low a value as desired orrpossi le. A fork assembly of this inventions-was brought to 0.225 10'.x negative and was for practicalpurposes, substantially permanent or perfect. The ultimate, with measurin instruments suiiicientl sensitive, would ge to obtain a value o zero for the temperature coefficient of frequency. The temperature coeicient of frequency of a tuning fork is equal to the temperature coefiicientof elasticity minus the temperature coefficient of expansion, divided by the factor 2, and is expressed by the formula:

Where is the temperature coeicient of frequency of the fork, y is the temperature coefficient' of the modulus of elasticity, and 2 is the temperature coeiicient of expansion.

The value y is negative and the value z is positive for steel, so that the two effects are additive, both causing the tem erature coso that these effects are subtractive. By

combining nickel-iron and carbon-steel in correct proportions2 the positive teniperatu e coeiiicient of elasticity of the nickel-iron counteracts the effect of the three other tem-l perature coeflicients. i

The forkof the present invention, is coinposed of about 1/10 part of steel having a temperature coefficient 'of elasticity of 34X10 and a temperaturecoeiiicient of expansion of 12 X 10,.and about 9/ 10 parts of invar'or elinvar having a temperature coeiiicient of elasticity of l50X 10 and a temperature coefficient of expansion of +6 10. The temperature coefcient, of frequency is the .summation of these. Such is represented by the equation This last value is practically a zero quantity, thus showing that the frequency of the fork is practically constant for any range'of temperature.

When the proportions are 10.7318% of.

steel and 89.2682% of invar or elinvar, this value becomes 0.000,000,000,03 and when the proportions are 10.7317% of steel and 89.26837 ofinvar or .elinvar, this value becomes +0.000,000,000,015. The absolute zero value u Juld Occur when the steel is between While I have herein described, and upon the drawing shown a few illustrative embodiments of the invention, it is to be understood that the latter is not limited thereto but may comprehend other constructions, details arrangements of parts, and features Without de arting from the spirit thereof;

aving thus disclosed the invention, I

claim:

1. A tuning fork composed of laminations of metals having opposite values for the temperature coefiicients of elasticity of said metals for maintaining the vibration frequency of the fork constant under changes l of temperature of the fork.

2. A tuning fork composed of laminations of metals having positive and ne peiature coefiicients of elasticity o the metals for maintaining the vibration frequency of the fork constant under changes of temperature of the fork.

3. A tuning fork composed of laminations of metals of which one metal has the propei'ty of varying the vibration frequency of the fork directly with the change in temperature of the forli, and another metal has the property of varying the vibration frequency of tlie fork inversely with the change in temperature of the fork, for maintaining' the vibration frequency of the fork constant iiiider changes of temperature of the fork.

4. A tuning fork composed of laminations of metals of which one metal has a temperature coeflicient of elasticity of a value equal to and opposite to the values of the temperature coefficient of elasticity of. the other metal and of the temperature coeieients of expansion of both metals.

5. -A tuning fork composed of of different metals temperature coeicients oi elasticity for giving to the fork a given vibration frequency which will remain constant under changes of temperature of the fork. i

6. A tuning fork composed of laminations of combined metals in the proportions of the coefiicients of elasticity values thereof, said values being op osite'. f

7. A tuning ork comprising laminations of diierent metals having opposite temperature coeicients of elasticity.

8. A tuning fork comprising laminations of different metals having opposite temperature coelicients of elasticity and in the. proportions ofthe values of said coeicients.

9. A tuning fork composed 'of steel and elinvar4 laminations.

10. A tuning fork composed of laminations in the proportions of about ten parts of elinvar andonepart of steel.

In witness whereof, I hereunto subscribe my name to this ication.

" B RT E. EISENHOUR.

laminations ative temhaving opposite values of' CERTIFICATE or CORRECTION.

Parent No. 1,880,923. october 4, w32.

A BERT E. EISENHOUR.

lt is hereby certified that error appears in the printed speeification ol the above numbered patent requiring correction as follows: Page 2, line 124. for 670" read "6700"; andthat-the said Letters Ratent should be read-with this correction therein thtthe same may conform to'the record of the case in the Patent Office.

Sizned'and sealed this 29th day of November, A. D. 1932.

. M.` J. Moore, (Seal) Ating Commissioner of Patents. 

